1. Field of the Invention
The present invention relates to an axial-flow fan and, more particularly, to an axial-flow fan that connects a plurality of rotor vanes in series in a single fan.
2. Description of the Related Art
The axial-flow fan is a popular fan device that has the features such as a simple structure, low cost, and a high air flow rate. These features have made it widely used in various systems as an air conditioning or ventilating device, for example, as the ventilation fan in a computer system.
In general, since the total pressure of the axial-flow fan is lower, the axial-flow fan cannot fully develop a high flow rate in a system of a high resistance. Therefore, in the case that a high total pressure is needed, two or more axial-flow fans are conventionally employed in series to provide the high total pressure.
Moreover, to avoid the interruption of operation due to the breakdown of the fans, a set of standby fan system is usually provided in series to the original fan system to avoid the system or device damage due to the interruption of the fan operation.
However, connecting two fans in series does not double the total pressure. Even if only one fan operates and the other stays still as a standby fan, the latter one reduces the total pressure of the fan in operation. The reason is that when the two fans are connected in series, the resistance between them increases and the operation efficiencies of them is decreased. Thus, in certain situations, for example in an air duct of an air conditioning system, the two axial-flow fans in series are separated far apart to minimize the interference between them. Nevertheless, this method is not feasible in the case that the installation space is limited.
Therefore, how to design an axial-flow serial fan with a plurality of rotor vanes that requires a small space and has the least interference effect becomes an important subject.